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Slimonia
Slimonia is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Slimonia have been discovered in deposits of Silurian age in South America and Europe. Classified as part of the family Slimonidae alongside the related Salteropterus, the genus contains three valid species, S. acuminata from Lesmahagow, Scotland, S. boliviana from Cochabamba, Bolivia and S. dubia from the Pentland Hills of Scotland and one dubious species, S. stylops, from Herefordshire, England. The generic name is derived from and honors Robert Slimon, a fossil collector and surgeon from Lesmahagow.
Out of the four described species of Slimonia, three measured below or up to 20 centimetres (7.9 in) in length. Only S. acuminata was larger, with the largest specimens measuring 100 centimetres (39 in) in length. Though this is large for a predatory arthropod, Slimonia would be exceeded in length by later and more derived (more "advanced") members of the closely related pterygotid family of eurypterids, which would become the largest known arthropods to ever live.
Slimonia is in many ways similar to the more derived (more "advanced") eurypterids of its superfamily, the Pterygotioidea. In particular, the expanded and flattened telson (the most posterior segment of the body) of Slimonia is similar to that of the pterygotid eurypterids and is a feature that Slimonia and the pterygotids only share with some derived hibbertopterid eurypterids (where the feature convergently evolved). The pterygotid telson was in general slightly larger than that of Slimonia and was more slender. The telson spike of Slimonia was much longer than any seen in the Pterygotidae (constituting just over half of the total telson length) however, serrated and ending in a fine point. The largest species of Slimonia, S. acuminata, reached a maximum length of 100 cm (39 in) whilst the smallest, S. dubia, grew to 12 cm (5 in) in length. Though 100 cm is large for a predatory arthropod, Slimonia would be exceeded in length by later and more derived (more "advanced") members of the closely related pterygotid family of eurypterids, which would become the largest known arthropods to ever live.
Slimonia can be distinguished from other members of its family, the Slimonidae, by a variety of characteristics. The prosoma (head) is quadrate (square-shaped) in shape and had small compound eyes on the frontal corners. The bodies were large and cordate (heart-shaped), with a narrow postabdomen and a telson with a strongly expanded anterior half. The chelicerae (frontal appendages) were small in comparison to those of the pterygotids and the walking legs had denticles, but no spines. Genital appendages were long and narrow in both males and females.
The type species of Slimonia, S. acuminata, was first described as a species of Pterygotus, "Pterygotus acuminata" (acuminata being Latin for "sharp" or "tapering"), by John William Salter in 1856, based on fossils recovered from deposits of Llandovery-Wenlock (Early to Middle Silurian) age in Lesmahagow, Scotland. That same year David Page erected a new genus to contain the species, as several distinctive characteristics made the species considerably different from other known species of Pterygotus, among them the shape of the carapace and S. acuminata lacking the large cheliceral claws known from Pterygotus. The generic name is derived from and honors Robert Slimon, a fossil collector and surgeon from Lesmahagow. Slimon was the first to discover eurypterid fossils in Lesmahagow, bringing them to the attention of Roderick Murchison in 1851. S. acuminata remains the largest known species, with the largest specimens measuring up to 100 cm (39 in) in length.
In 1899, an additional species, S. dubia, would be referred to the genus. This species was recovered from slightly earlier deposits (Llandovery age) in the Pentland Hills of Scotland and could be distinguished from S. acuminata by the more elongated telson (also not as broad in the parts furthest back), thinner telson spike and a slightly different, tapering, body shape that tapers evenly the whole way instead of suddenly narrowing near the seventh segment as in S. acuminata. The type specimen of S. dubia is a badly preserved carapace, with fragments of various degrees of completion of the first eleven segments found associated. Despite its fragmentary nature, the quadrangular (square) shape of the carapace and the eyes placed at its corners allowed zoologist and paleontologist Malcolm Laurie to place it within Slimonia when describing it in 1899. The size of the carapace suggests that the species would have grown to 12 cm (5 in) in length.
Another species, S. stylops, was first considered a species of Pterygotus when described by John William Salter in 1859, and the highly fragmentary nature of the known fossils make a precise identification difficult and problematic. Only one specimen, the anterior part of a carapace with the compound eyes placed on the margin, is known and though it does resemble Slimonia, it could also potentially be referred to Hughmilleria or even represent the carapace of Salteropterus abbreviatus (a closely related slimonid eurypterid known only from the telson and metastoma, a large plate part of the abdomen). The fossils were recovered from deposits of Pridoli (Late Silurian) age in Herefordshire, England and suggest that the species grew to 12 cm (5 in) in length. Due to its problematic nature, S. stylops is seen as a nomen dubium by modern researchers.
In 1973, another species of Slimonia was named by Kjellesvig-Waering based on one single fossil recovered by Eduardo Rodriguez from the Kirusillas Formation, of Ludlow-Pridoli (Late Silurian) age, in Cochabamba, Bolivia. Named S. boliviana, the holotype (BLV15, deposited at the National Museum of Natural History of France) comprises a well-preserved telson typical of the genus, being laterally inflated and with a dagger-like terminal point. It was anteriorly covered with small scales semilunar to mucronitic ("spined") grouped into a single row of large marginal scales that form a linear serrated edge. A slight dorsal keel is present along the telson. There was a triangular area at the base of the telson which could have been a point of union with the muscles. S. boliviana differed from S. acuminata in having the keel much less developed, narrower and not reaching the terminal spike. The latter was wider, not as pointed and with less developed serrations. The telson itself was wider and shorter than in the type species. This species was the third Silurian eurypterid in the Southern Hemisphere to be described, the other two coming from Australia. The fossil suggest a total body length of 20 centimetres (7.9 in).
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Slimonia
Slimonia is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Slimonia have been discovered in deposits of Silurian age in South America and Europe. Classified as part of the family Slimonidae alongside the related Salteropterus, the genus contains three valid species, S. acuminata from Lesmahagow, Scotland, S. boliviana from Cochabamba, Bolivia and S. dubia from the Pentland Hills of Scotland and one dubious species, S. stylops, from Herefordshire, England. The generic name is derived from and honors Robert Slimon, a fossil collector and surgeon from Lesmahagow.
Out of the four described species of Slimonia, three measured below or up to 20 centimetres (7.9 in) in length. Only S. acuminata was larger, with the largest specimens measuring 100 centimetres (39 in) in length. Though this is large for a predatory arthropod, Slimonia would be exceeded in length by later and more derived (more "advanced") members of the closely related pterygotid family of eurypterids, which would become the largest known arthropods to ever live.
Slimonia is in many ways similar to the more derived (more "advanced") eurypterids of its superfamily, the Pterygotioidea. In particular, the expanded and flattened telson (the most posterior segment of the body) of Slimonia is similar to that of the pterygotid eurypterids and is a feature that Slimonia and the pterygotids only share with some derived hibbertopterid eurypterids (where the feature convergently evolved). The pterygotid telson was in general slightly larger than that of Slimonia and was more slender. The telson spike of Slimonia was much longer than any seen in the Pterygotidae (constituting just over half of the total telson length) however, serrated and ending in a fine point. The largest species of Slimonia, S. acuminata, reached a maximum length of 100 cm (39 in) whilst the smallest, S. dubia, grew to 12 cm (5 in) in length. Though 100 cm is large for a predatory arthropod, Slimonia would be exceeded in length by later and more derived (more "advanced") members of the closely related pterygotid family of eurypterids, which would become the largest known arthropods to ever live.
Slimonia can be distinguished from other members of its family, the Slimonidae, by a variety of characteristics. The prosoma (head) is quadrate (square-shaped) in shape and had small compound eyes on the frontal corners. The bodies were large and cordate (heart-shaped), with a narrow postabdomen and a telson with a strongly expanded anterior half. The chelicerae (frontal appendages) were small in comparison to those of the pterygotids and the walking legs had denticles, but no spines. Genital appendages were long and narrow in both males and females.
The type species of Slimonia, S. acuminata, was first described as a species of Pterygotus, "Pterygotus acuminata" (acuminata being Latin for "sharp" or "tapering"), by John William Salter in 1856, based on fossils recovered from deposits of Llandovery-Wenlock (Early to Middle Silurian) age in Lesmahagow, Scotland. That same year David Page erected a new genus to contain the species, as several distinctive characteristics made the species considerably different from other known species of Pterygotus, among them the shape of the carapace and S. acuminata lacking the large cheliceral claws known from Pterygotus. The generic name is derived from and honors Robert Slimon, a fossil collector and surgeon from Lesmahagow. Slimon was the first to discover eurypterid fossils in Lesmahagow, bringing them to the attention of Roderick Murchison in 1851. S. acuminata remains the largest known species, with the largest specimens measuring up to 100 cm (39 in) in length.
In 1899, an additional species, S. dubia, would be referred to the genus. This species was recovered from slightly earlier deposits (Llandovery age) in the Pentland Hills of Scotland and could be distinguished from S. acuminata by the more elongated telson (also not as broad in the parts furthest back), thinner telson spike and a slightly different, tapering, body shape that tapers evenly the whole way instead of suddenly narrowing near the seventh segment as in S. acuminata. The type specimen of S. dubia is a badly preserved carapace, with fragments of various degrees of completion of the first eleven segments found associated. Despite its fragmentary nature, the quadrangular (square) shape of the carapace and the eyes placed at its corners allowed zoologist and paleontologist Malcolm Laurie to place it within Slimonia when describing it in 1899. The size of the carapace suggests that the species would have grown to 12 cm (5 in) in length.
Another species, S. stylops, was first considered a species of Pterygotus when described by John William Salter in 1859, and the highly fragmentary nature of the known fossils make a precise identification difficult and problematic. Only one specimen, the anterior part of a carapace with the compound eyes placed on the margin, is known and though it does resemble Slimonia, it could also potentially be referred to Hughmilleria or even represent the carapace of Salteropterus abbreviatus (a closely related slimonid eurypterid known only from the telson and metastoma, a large plate part of the abdomen). The fossils were recovered from deposits of Pridoli (Late Silurian) age in Herefordshire, England and suggest that the species grew to 12 cm (5 in) in length. Due to its problematic nature, S. stylops is seen as a nomen dubium by modern researchers.
In 1973, another species of Slimonia was named by Kjellesvig-Waering based on one single fossil recovered by Eduardo Rodriguez from the Kirusillas Formation, of Ludlow-Pridoli (Late Silurian) age, in Cochabamba, Bolivia. Named S. boliviana, the holotype (BLV15, deposited at the National Museum of Natural History of France) comprises a well-preserved telson typical of the genus, being laterally inflated and with a dagger-like terminal point. It was anteriorly covered with small scales semilunar to mucronitic ("spined") grouped into a single row of large marginal scales that form a linear serrated edge. A slight dorsal keel is present along the telson. There was a triangular area at the base of the telson which could have been a point of union with the muscles. S. boliviana differed from S. acuminata in having the keel much less developed, narrower and not reaching the terminal spike. The latter was wider, not as pointed and with less developed serrations. The telson itself was wider and shorter than in the type species. This species was the third Silurian eurypterid in the Southern Hemisphere to be described, the other two coming from Australia. The fossil suggest a total body length of 20 centimetres (7.9 in).
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